How to loop through an array

Question

for i in range(len(a)):
    a = a[i-2]
    print(a)

IndexError: invalid index to scalar variable

So I am getting this index error, when i am trying to loop through my array. A is my array. I looked up the error invalid index to scalar variable online but it looks like its a case by case basis. Any help would be greatly appreciated. Ive tried replacing the for loop to this:

for i in range(len(a)):
    a = a(i-2)
    print(a)

But that doesn't work and throws up this error.

'numpy.ndarray' object is not callable

Eric M · Accepted Answer · 2020-04-02 21:22:05Z

1

You should generally not attempt to change the variable you are looping over. Here you are looping over a and then changing a at each iteration of the loop.

This will work though

a = [1,2,3,4,5]

for i in range(len(a)):
    print(a[i-2])

You probably need to include an explanation of what it is you are trying to achieve so people can better help you.

answered Apr 2, 2020 at 21:22

Eric M

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user3842413 · Accepted Answer · 2020-04-02 21:23:52Z

1

In addition to Eric's answer, you should be modifying the [i-2] part since that you'll end up trying to access an invalid element like a[-1]

answered Apr 2, 2020 at 21:23

user3842413

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Matt · Accepted Answer · 2020-04-02 21:26:59Z

1

Assuming a=[1,2,3,4], if you do

for i in range(len(a)):
 b = a[i]
 print(b)

should output

There were a two issues from what I could tell.

you overwrite a after your first loop (a goes from array to scalar)
you were using the indices (0,1,2,3) to ask for positions -2,-1, 0, 1 of the a array. Note the first two don't exist.

answered Apr 2, 2020 at 21:26

Matt

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